Recruitment of the immune system to sites of tumor growth for the purpose of initiating an anti-tumor antigen response is a promising approach to cancer treatment. [U. Galili, K. Wigglesworth and U. M. Abdel-Motal, J. Immunology, 2007, 178, 4676-4687; C. B. Carlson, P. Mowery, R. M. Owen, E. C. Dykhuizen and L. L. Kiessling, ACS Chem. Biol., 2007, 2, 119-127; R. P. Murelli, A. X. Zhang, J. Michel, W. L. Jorgensen and D. A. Spiegel, J. Am. Chem. Soc., 2009, 131, 17090-17092; M. Popkov, B. Gonzalez, S. C. Sinha and C. F. Barbas, Proc. Natl. Acad. Sci. USA 2009, 106, 4378-4383.]
The ability to recruit endogenous antibodies to tumor sites allows for clearance of targeted cells through both complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC). CDC is promoted primarily by antibodies of the IgM isotype; decoration of cells with sufficient levels of antibody leads to activation of the classical complement cascade to form pores in the target cell membranes and release cytokines which attract immune cells. ADCC is dependent on the activation of NK and other immune effector cells through ligation of their activating Fc receptor (FcγRIII) by IgG antibodies. CDC and ADCC are linked; soluble factors released during complement activation recruit effector cells for ADCC, thus activation of both pathways is beneficial for optimal tumor clearance. In addition to effecting tumor removal, these methods have the potential to prime the immune system to recognize tumor-associated antigens in the future, in essence, forming an in situ autologous vaccine [D. Berd, Vaccine 2001, 19, 2565-2570; U. Galili, M. R. Albertini, P. M. Sondel, K. Wigglesworth, M. Sullivan and G. F. Whalen, Cancers, 2010, 2, 773-793.]
By tagging tumor cells with a widely-recognized foreign antigen, serum antibodies of both IgG and IgM isotype will bind and initiate immune responses leading to both tumor clearance and immune system priming. This approach requires a suitable antigen for antibody recruitment and a method to tag the desired cells.
The ideal antigen for such methods would be recognized by a majority of the target population (e.g., humans) without prior vaccination, and would be able to recruit both IgG and IgM classes. The antigen Gal-α-1,3-Gal (herein called αGal) is recognized as having these properties. This antigen is present in much of nature with the striking exceptions of humans, chimps, and old world monkeys. As such, humans are frequently exposed to this carbohydrate and develop fairly high, stable titers of both IgG and IgM isotypes against it.
One method of cell tagging takes advantage of the propensity of exogenously added lipids to partition into nearby cell membranes. For example, certain αGal lipids were isolated from rabbit erythrocytes and injected intratumorally. The injected lipids were reported to insert into tumor membranes forming a display of antigenic carbohydrates [U. Galili, K. Wigglesworth and U. M. Abdel-Motal, 2007, 178, 4676-4687]. This approach using certain αGal lipids has been reported to be successful in both mouse models and the clinic. See also U.S. Pat. Nos. 7,820,628; 6,361,775; and 5,879,675. A second tagging approach uses small molecules to target upregulated tumor surface receptors. Both αvβ3 integrins and PSMA (prostate-specific membrane antigen) have been targeted in this manner; however, robust cell killing under physiologically relevant conditions has not yet been achieved [C. B. Carlson, P. Mowery, R. M. Owen, E. C. Dykhuizen and L. L. Kiessling, 2007, ACS Chemical Biology 2, 119-127; R. P. Murelli, A. X. Zhang, J. Michel, W. L. Jorgensen and D. A. Spiegel, J. Am. Chem. Soc. 2009, 131, 17090-17092.]
Recent microarray studies profiling human serum antibodies to various carbohydrates have identified rhamnose as a molecule of interest. Anti-rhamnose was reported to be present in a greater number of serum samples, and was reported to be more abundant than anti-Gal [M. E. Huflejt, M. Vuskovic, D. Vasiliu, H. Xu, P. Obukhova, N. Shilova, A. Tuzikov, O. Galanina, B. Arun, K. Lu and N. Bovin, Mol. Immunol. 2009, 46, 3037-3049, O. Oyelaran, L. M. McShane, L. Dodd and J. C. Gildersleeve, J. Proteome Res. 2009, 8, 4301-4310] In addition, it was reported that normal strains of lab mice can be immunized against rhamnose to create a model system without the need for special knockout animals [W. Chen, L. Gu, W. Zhang, E. Motari, L. Cai, T. J. Styslinger and P. G. Wang, ACS Chem. Biol. 2011, 6, 185-191.]
The present invention relates to the use of L-rhamnose antigen-lipid conjugates to recruit anti-L-Rha antibodies to cells to initiate an anti-cell antigen response. In particular, the cells are tumor cells and use of the L-rhamnose antigen-lipid conjugates activates the complement pathway, induces complement-mediated cell death and initiates cell-dependent cytotoxic pathways, such as cytotoxic T cell response.